The present invention pertains to the surface treatment of cold-embrittled parts. Surface treatment is used to refer to deburring, lacquer removal, separation and stripping, as well as hardening and polishing.
A great number of devices are known for the surface treatment of cold-embrittled parts. A conveyer means by which the parts are conveyed and rotated, as well as a spray means for a low boiling, liquefied gas, usually nitrogen, and at least one centrifuge wheel for a jet material, e.g., cast steel or plastic granules, are common features of all these devices. The known conveying means include especially rotary drums, belts circulating in a drum-like manner, or rotary plates. A device for deburring parts is known from West German Offenlegungsschrift No. 26 50 202, in which the parts are moved on a cradle which is equipped with screens for separating granulate, coarse chips and dust. The device is equipped with at least one centrifuge wheel throwing off granulate in horizontal direction. The centrifuge wheel is surrounded by a conical deflecting collar ring with a cone angle of 90.degree.. The granulate thrown off horizontally is reflected by this deflecting collar ring downward to the work surface of the cradle. The nozzles for the low boiling liquefied gas are disposed at the edge of the deflecting collar ring. The surface treatments of cold-embrittled parts which are to be carried out normally can be performed with this prior art device in a satisfactory manner. The only exception is small and delicate parts which must be treated rapidly and gently and which are normally produced in small batches only. Even though the prior art device guarantees that the kinetic energy of the granulate striking the work surface is equal in all points, it is inevitable that the parts are subject to the jet treatment for different lengths of time depending on their position on the work surface, this is irrelevant in most surface treatment operations as long as the desired effect, e.g., complete deburring, is achieved. However, delicate, small parts are sensitive to differences in the jet treatment time. It has also been found that such parts can become damaged due to another effect in certain cases.
The granulate used for the jet treatment is always recirculated, which requires the separation of dust and coarse chips. However, the chips whose size corresponds to the size of the grains of the granulate are not separated in this process. Together with the original granulate, these chips are involved in the jet treatment and become gradually shattered completely only after several cycles. This is usually completely irrelevant for the surface treatment. However, if these chips are harder or have a higher density than the granulate, they can damage delicate, small parts or parts with sensitive surfaces.